Biology Unit 3

Life processes 2 and Microorganisms

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Gas and solute exchange

- Substances move by diffusion, osmosis and active transport.

- Diffusion is the movement of particles from high concentration to low concentration.

- Osmosis is particles from high water concentration to low water concentration across a partially permeable membrane.

- Active transport is the movement against a concentration gradient, requiring energy.

- Exchange surfaces are adapted to maximise effectiveness

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Structure of Leaves

- Carbon Dioxide diffuses into air spaces within the leaf, then it diffuses into cells where photosynthesis happens. The leafs structure is specially adapted for this.

- The underneath of a leaf is the exchange surface and is covered in tiny holes called stomata where the carbon dioxide diffuses through.

- Water vapour and oxygen also diffuse out through the stomata.

- The size of the stomata is controlled by the guard cells. These close the stomata if the plant is losing too much water (wilt) and open if there is excess. 

- The flattened shape of the leaf increases the area of the exchange surface so it's more effective.

- The walls of the cells inside the leaf form another exchange surface. The air spaces in the leaves increase the area of the surface so there's more chance for carbon dioxide to get into the cells.

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Active Transport

Root hairs are specialised for absorbing water and minerals

- The cells on the surface of plants roots grow into 'hairs' which stick out into the soil.

- This gives the plant a big surface area for absorbing water and mineral ions.

- The concentration of minerals is usually higher in the root hair cell than the soilso active transport is needed.

- This requires energy from respiration to make it work.

- A.T is used in thee gut when there is a low concentration of nutrients, but a high concentration in the blood.

- They diffuse naturally when the concentration is higher in the gut but it has to happen the other way round when it is lower.

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The circulation system

- The circulation systems main function is to get food and oxygen to every cell in the body but is also a waste collection service.

Double circulation system

 - The heart has 2 pumps. The right side pumps deoxygenated blood to the lungs to collect oxygen and remove carbon dioxide. The left side then pumps this around the whole body.

- Arteries carry blood away from the heart at high pressure.

- Arteries carry oxygenated blood and veins carry deoxygenated blood. The pulmonary artery and pulmonary veins are the exception to this rule.

- The arteries eventually split off into thousands of capillaries which take blood to every cell in the body.

- The veins then collect the 'used' blood and carry it back to the heart at low pressure to be pumped back round again.

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- Capillaries use diffusion to deliver food and oxygen direct to body tissues and take carbon dioxide away.

- Their walls are usually one cell thick to make it easier for things to pass through.

- Blood is made of 4 main parts: White blood cells, Red blood cells, Plasma and Platelets (small fragments of cells that help blood to clot at a wound).

- RBC carry oxygen from the lungs to the cells of the body. They have a concave shape to maximise surface area for absorbing oxygen.

- No nucleus so more room for haemoglobin. In the lungs, haemoglobin combines with oxygen to form oxyhaemoglobin and in the body tissues the reverse happens to release oxygen into the cells.

- Plasma is a straw-coloured liquid which carries: Red and white blood cells and platelets. Nutrients like glucose and amino acids, carbon dioxide from organs to lungs, urea from liver to kidneys, hormones, and antibodies and antitoxins produced by white blood cells.

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- Muscles are made of muscle cells which use oxygen to release energy from glucose (respiration)  which is used to contract the muscles.

- Increase in muscle activity requires more glucose and oxygen so more carbon dioxide needs to be removed from muscle cells so blood flows at a faster rate.

- This is why physical activity: Increases breathing rate, increases the speed the heart pumps, and dilates the arteries which supply blood to the muscles.

- Glycogen is used during exercise.

- Some glucose from food is stored as glycogen.

- It is mainly stored in the liver but each muscle also has it's own store.

- During vigorous exercise, muscles use glucose rapidly and need to draw from glycogen stores to provide more energy.

- When glycogen stores get low, the muscles begin to get tired.

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Anaerobic respiration is used if there's not enough oxygen.

- This is the breakdown of glucose....Glucose --> Energy + Lactic acid

- This is not the best way to convert glucose to energy as a build up of lactic acid in the muscles is painful so the muscles get tired.

- Anaerobic respiration leads to oxygen debt.

- This means you have to 'repay' the oxygen that didn't get into the muscles in time which means you have to breathe hard for a while after you stop.

- Although high levels of CO2 and lactic acid are detected by the blood, the pulse and breathing rate stay high to try and rectify the situation.

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- Nephrons are the filtration units in the kidneys

- Ultrafiltration - A high pressure is built up which squeezes water, urea, ions and sugar out of the blood into the Browmans capsule.

- The membranes between the blood vessels and capsule act like filters, so big molecules like proteins are not squeezed out and stay in the blood.

Re-absorption - As liquid flows along the nephron, useful substances are re-absorbed back into the blood.

- All the sugar is re-absorbed. This involves the process of active transport against the concentration gradient. Sufficient Ions and water are reabsorbed and excess ions are not.

- Release of wastes: The remaining substances continue out of the nephron, into the ureter and down to the bladder as urine. 

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Kidney failure

- If the kidneys don't work properly then the waste substances build up and this results in death.

- People with kidney failure can be kept alive by dialysis treatment.

- Dialysis is doe 3-4 times a week for 6 hours and usually at night as patients cant move much during it. It is done to keep concentration of dissolved substances at normal levels and to remove waste substances.

- In a dialysis machine, the patients blood flows alongside a partially permeable membrane along the other side of which is the dialysis fluid.

- It is permeable to things such as ions and waste substances, but not big molecules like protein.  The dialysis fluid contains the same concentrations of dissolved ions and glucose as in healthy blood. 

- Only waste substances and excess ions and water diffuse across the membrane.

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Kidney transplant

Transplanted organs can be rejected by the body

- The only current cure for kidney disease is to have a kidney transplant.

- The immune system in the body can reject the organ so to prevent this, precautions are taken:

  • A donor with the tissue type that closely matches the patients is chosen
  • The patients bone marrow is zapped with radiation to stop white blood cells being produced so antibodies wont attack the kidney.
  • This does however mean the patient can't fight any infection that comes along, so they must be kept in total sterile conditions until the operation.
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Food and drink from microorganisms

- People used to think that life could spontaneously generate from non-living material.

- It was an experiment using a swan-necked flask (where no microbes could get in) where a boiled broth didn't go off, proving it is microbes that cause it to go off, not air.

- Most cheese is made using bacteria...

- A culture of bacteria is added to milk which produces solid curds. These are the separated from the liquid whey. More bacteria are sometimes added and the whole lot is left to ripen for a while. Moulds are added to give Blue cheese its colour and taste.

- Yoghurt is also made using bacteria...

- Milk is often heat treated to kill off any bacteria, then cooled. A starter culture of bacteria is added and these ferment the lactose sugar to lactic acid. The acid causes the milk to clot and turn into yoghurt. Sterilised flavours are then added.

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Using yeast

Yeast is a single-celled fungus - It is a micro-organism

Yeast can respire without any oxygen, this is known as fermentation

Glucose---> Ethanol + Carbon Dioxide + Energy

Yeast can also respire aerobically which produces more energy

Glucose + Oxygen ----> Carbon Dioxide + Water + Energy

Yeast is used in dough to convert sugars to carbon dioxide (and some ethanol). It is carbon dioxide that makes bread rise, as it expands, it gets trapped in the dough, making it lighter.

It is also used to make alcoholic drinks...

Beer is made from grains, the grains germinate for a few days, during which the starch in them is broken down to sugar by enzymes and they are then dried in a kiln (malting). They are then mashed up and water is added to make a sugary solution which is then sieved to remove bits. The sugary solution is then fermented by yeast, turning the sugar into alcohol.

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Micro-organisms in industry

Micro-organisms are grown in fermenter's on a large scale.

- A fermenter is a large container full of liquid culture medium where micro-organisms can grow and reproduce.


1) Food is provided in a liquid culture medium.

2) Air is piped in to supply oxygen to the micro-organisms.

3) They need to be kept at the right temperature, they produce heat when they reproduce so the fermenters must be cooled (water cooled jacket).

4) The right PH is needed as micro-organisms will thrive on this.

5) Sterile conditions are also needed to prevent contamination.

6) Micro-organisms must be kept from sinking to the bottom so a motorised stirrer is needed.

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Fuels from micro-organisms

Ethanol is made by anaerobic fermentation of sugar...

Yeast makes ethanol when it  breaks down glucose...

Glucose ---> Ethanol + Carbon Dioxide + Energy

The ethanol is distilled to separate it from the yeast and remaining glucose

Biogas is made from anaerobic fermentation of waste material...

70% methane, 30% carbon dioxide. It is produced in a simple fermenter called a digester or generator. It can't be stored as liquid so must be used instantly.

Fuel production can happen large scale or small scale...

Large scale generators are being set up in lots of countries. Small scale generators are used to make gas for a village or family for cooking stoves etc.

Human waste, animal waste and food waste can be digested by bacteria to produce biogas. By-products are used to fertilise crops and gardens.

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Fuels from micro-organisms

- Batch generators  make biogas in small batches - manually loaded with waste.

- Continuous generators make biogas all the time - waste is continuously fed in.

No matter what type of generator it is, it must have the following:

1) An inlet for waste material

2) An outlet for digested material to be removed through

3) An outlet for biogas to be piped down

Factors to consider when designing a generator:

  • Cost 
  • Convenience - batch is less convenient as they must be loaded, emptied and cleaned.
  • Efficiency - gas may need to be kept warm which will cost money.
  • Position - waste will smell so generators shouldn't be near homes.
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- Greener alternative to fossil fuels, carbon dioxide released was taken from plants so they are carbon neutral.

- Doesn't produce significant amounts of sulfur dioxide or nitrogen oxides which cause acid rain.

- Raw material is cheap and readily available

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Using micro-organisms safely

Micro-organisms are grown on agar jelly in a Petri dish 

- They are grown in a culture medium.

- Sometimes need carbohydrates as an energy source, plus mineral ions.

- Agar jelly can be poured when hot, and sets when cold.

Equipment must be sterilised to prevent contamination...

- If it's not sterilised, unwanted micro-organisms may grow and contaminate it.

- Unwanted substances could make harmful substances or cause disease.

- Petri dishes and the growth medium must be sterilised.

- Inoculating loops are sterilised by being passed through a flame.

- The Petri dish must have a lid to stop any micro-organisms getting in.

- In schools, temp is kept low so harmful pathogens cant grow.

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The breathing system

The lungs are in the Thorax

- Thorax is the top part of your body and is separated from the lower part by the diaphragm. 

- The air that you breathe goes through the trachea which splits into two tubes called 'bronchi', one going to each lung.

- The bronchioles finally end at small bags called alveoli where the gas exchange takes place.

Breathing in...

Inter-coastal muscles and diaphragm contract, thorax volume increases which decreases pressure and draws air in.

Breathing out...

Opposite of above ^^

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Diffusion through cell membranes

- The lungs transfer oxygen to the blood and remove carbon dioxide from it.

- Alveoli are specialised to maximise diffusion of oxygen and CO2...

  • enormous surface area
  • Moist lining for dissolving gases
  • Very thin walls
  • Copious blood supply

The villi provide a really big surface area...

 - The inside of the small intestine is lined with millions of Villi.

 - They increase surface area massively so the food is absorbed much quicker into the blood.

They have: A single layer of surface cells and a very good blood supply to assist quick absorption. 

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CHloe, you are my favourite person in the world and I hope you don't mind if I use these?

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